In the Zend Server UI, navigate to Administration > Components > Zend OPcache. Set the directive opcache.dups_fix to ON. Click the save button near the top of the page. Restart Zend Server via the icon at the top right.

Details

In older versions of Zend Server, you may see the text listed as "Optimizer+" instead of "OPcache".

A full description of the page can be found in the OPcache Duplicate Functions Fix section of the documentation page Working with OPcache